Investigation Of Structure And Magnetic Properties Of Double Perovskite Based On Ni(Co)-Mn By First-principles

With the development of computer science and technology,materials science,physics,and computer science are increasingly connected.Solving complex physical problems in material systems through computer technology has become one of the most important research methods.The double perovskite oxide materials with a general formula of A2BB'O6 have become one of the research hot topic in the field of the materials science and condensed matter physics because of their special crystal structure and excellent physical properties.With the rapid development of related theory and material calculation software,theoretical calculation has become an important research method in the fields of materials,physics and chemistry.In this paper,the Ni(Co)-Mn-based double perovskite oxide La2MnCoO6 and La2MnNiO6 are chosen as the research objects by using the first-principles calculation software VASP package based on density functional theory.Subsequent calculations investigated the two oxides after the alkaline earth metal Ca doping.The results are analyzed from three aspects of crystal structure,electronic structure and magnetic properties.The crystal structure parameters of LMCO and LMNO can be obtained accurately by GGA.But electronic structure of LMCO is obtained accurately by GGA+U.The band gap is 0.91 eV when U is 3 eV,and as the U value increases to 6 eV,the band gap increases to 1.38 eV.As the U value increases,the total magnetic moment of LMCO is increased from 5.797?B/f.u.to 5.924?B/f.u.,but the total magnetic moment of LMNO remains almost unchanged at 5 ?B/f.u..With the doping of Ca atom at La site in LMCO,the unit cell volume,Co-O bond length and CoO6 octahedral volume decrease,while the Mn-O bond length and MnO6 octahedral volume remain unchanged.Simultaneously,spin states are found at Fermi level,indicating a change in the ground state.But,the semi-metallic properties are exhibited when the doping concentration is 25%and 75%.Magnetic are also very different between the GGA method and the GGA+U method.And total magnetic moment varies with Co atomic magnetic moment.The total magnetic moment decreases rapidly by GGA.However,the total magnetic moment shows an increasing trend by GGA+U.The unit cell volume,Ni-O bond length and NiO6 octahedral volume of Ca-doped LMNO decrease with increasing concentration.The electronic structure exhibits spin polarization at the Fermi level,exhibiting semi-metallic properties.The total magnetic moment of the system is also linearly reduced with the increase of the Ca doping concentration.And total magnetic moment varies with Ni atomic magnetic moment.After Sr doping,a result consistent with Ca doping was obtained.However,there is almost no difference in the total magnetic moment by doping Sr atoms and Ca atoms.